System for analyzing impact and puncture resistance

ABSTRACT

A method and a system for analyzing a physical characteristic of a film sample are described herein. The system includes a material holder system configured to hold the film sample; a dart testing system configured to test a physical characteristic of the film sample; and a moving system configured to move the held film sample to be analyzed or tested between stations. The moving system is configured to move the held film sample in the material holder system to the dart testing system.

FIELD

The present invention relates to a system and process for analyzingimpact and puncture resistance of a film or sheet of material.

INTRODUCTION

Characterizing physical properties of materials is useful in analyzingand improving chemical formulations employed in the production of thematerials as well as in analyzing and improving processes ofmanufacturing the materials. Characterizing the physical properties mayalso help consumers determine the best product for their particular usecase, as well as help researchers develop novel solutions for specificapplications. One of the useful physical properties of a material isdetermining puncture properties of the material. A dart test providesscientists insight into the high speed puncture properties of amaterial. A dart test usually involves piercing a thin film with arounded cylindrical probe of specific dimensions that is traveling at aspecific speed and measuring a force exerted by the probe on the thinfilm.

Currently, dart testing on films is performed in two ways: the manualdrop-dart system and the instrumented dart system. In both cases thesystem relies on gravity to accelerate the dart probe towards the filmto be tested. The film is held taut in place by means of clampingmechanisms. The drop dart (DD) involves dropping a known mass/weightonto the film. An operator makes an observation of whether the film waspunctured. This test can be repeated numerous times with differentmasses/weights on multiple replicates of the film. The resulting filmproperties (usually only the overall energy) is estimated from theresults. However, this system is cumbersome to use, not suited forautomated operation, and does not provide a detailed understanding ofthe nature of a force curve applied to the film.

The instrumented dart impact system (IDI) is better suited to obtainricher data from a single test by incorporating a force sensor on thedart probe used to puncture the film. This is the currentstate-of-the-art for automated dart systems. However, even with thissystem, the loading and unloading of films is performed manually. Inaddition, this system provides a limited amount of collected data.

Therefore, a need remains for an automated process and system foranalyzing impact and/or puncture resistance of a film of material.

SUMMARY

It was determined that by using a system and method for analyzing impactand/or puncture resistance according to the present disclosure, theprocess is automated, throughput is increased, and the amount of datagathered from testing is improved.

An aspect of the present disclosure is to provide a system for analyzinga physical characteristic of a film sample. The system includes amaterial holder system configured to hold the film sample; a darttesting system configured to test a physical characteristic of the filmsample; and a moving system configured to move the held film sample tobe analyzed or tested between stations. The moving system is configuredto move the held film sample in the material holder system to the darttesting system.

Another aspect of the present disclosure is to provide a method foranalyzing a physical characteristic of a film sample. The methodincludes holding the film sample by a material holder system connectedto a moving system; moving the film sample by the moving system to adart testing system; and testing a physical characteristic of the filmof the material using the dart testing system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, as well as the methods of operation andfunctions of the related elements of structure and the combination ofparts and economies of manufacture, will become more apparent uponconsideration of the following description and the appended claims withreference to the accompanying drawings, all of which form a part of thisspecification, wherein like reference numerals designate correspondingparts in the various figures. It is to be expressly understood, however,that the drawings are for the purpose of illustration and descriptiononly and are not intended as a definition of the limits of theinvention.

FIG. 1 shows a schematic diagram of a system according to an embodimentof the present disclosure;

FIG. 2 shows a three-dimensional perspective view of a robotic system,according to an embodiment of the present disclosure;

FIG. 3 shows a three-dimensional perspective view of a material holdersystem, according to an embodiment of the present disclosure;

FIG. 4 shows a three-dimensional perspective view of components of athickness measurement system, according to an embodiment of the presentdisclosure;

FIG. 5 shows a three-dimensional perspective view of a material imageanalyzer system for analyzing defects in the film sample, according toan embodiment of the present disclosure;

FIG. 6A is a three-dimensional perspective view of a clamping system,according to an embodiment of the present disclosure;

FIG. 6B shows a cut-away view of the clamping system, according to anembodiment of the present disclosure;

FIGS. 7A and 7B show initial and final frames of a video of a filmsample clamped by a clamp assembly, according to an embodiment of thepresent disclosure;

FIGS. 8A and 8B show frames from the film sample when a dart juststrikes the film sample (FIG. 8A) and when the film sample is stretchedthe most (just before puncture) (FIG. 8B), according to an embodiment ofthe present disclosure;

FIG. 9 shows a three-dimensional perspective view of a dart probemechanism, according to an embodiment of the present disclosure;

FIG. 10 shows a three-dimensional perspective view of a dart probe,according to an embodiment of the present disclosure;

FIGS. 11A and 11B show side views of the film sample clamped by theclamp just before the dart probe comes into contact with the film sampleand after the dart probe comes in contact with the film sample andstretches the film to a maximum just before puncture, respectively,according to an embodiment of the present disclosure;

FIG. 12A is a plot of the force (N) exerted on the probe versus time (s)from a start of the movement of the probe to a complete stop of theprobe, according to an embodiment;

FIG. 12B is a plot of the force (N) exerted on the probe versus time (s)from the impact point with the film sample to completion of puncture ofthe film sample, according to an embodiment of the present disclosure;

FIGS. 13A and 13B show plots of the force (N) versus displacement (m),according to an embodiment of the present disclosure;

FIG. 14 shows the robotic system picking up the film sample using thematerial holder system, according to an embodiment of the presentdisclosure;

FIG. 15 shows measuring a thickness of the sample using a materialthickness measurement system, according to an embodiment of the presentdisclosure;

FIG. 16 shows performing a defect analysis using a material imageanalyzer system, according to an embodiment of the present disclosure;

FIG. 17A shows the robotic system picking up a tested film sample from adart testing system, according to an embodiment of the presentdisclosure;

FIG. 17B shows the robotic system placing a new untested film sample inthe dart testing system, according to an embodiment of the presentdisclosure; and

FIG. 18 shows the robotic system disposing of the tested film sample.

DETAILED DESCRIPTION

According to embodiments of the disclosure, the process of testingimpact and puncture resistance of a thin film of material may beautomated. The idea for automated dart testing systems arises from aneed for high throughput (HTP) testing in various industries. A higherrate of testing large amounts of materials and obtaining data that canbe gathered relatively quickly and analyzed for trends, allows moredetailed studies to be conducted on areas of interest. One featureneeded in the inception of an HTP testing setup is a continuous (or nearcontinuous) operation. By allowing systems to run non-stop, it increasesthe amount of testing performed. The system also allows increase ofincreasing the speed of a single test as compared to manual testingsystems. This is accomplished using robotics to take the place of ahuman researcher or operator, as robots can run for longer periods oftime without interruption. A second feature that may be used forincreasing throughput of a system without sacrificing accuracy is toperform multiple tests in parallel. A third feature is that the systemis repeatable and uniform as compared to human-based testing systems.Embodiments of the present disclosure employ these features to provide atesting setup that can greatly increase the number of samples tested.

In addition to being integrated with the blown film fabrication line,the present system for analyzing impact and puncture resistance of thinfilms can also be integrated into existing blown film labs. By beingable to conduct tests automatically and relatively quickly, the labswould be able to clear out their backlog of tests using the presentsystem.

Furthermore, the present system allows testing various films of materialincluding testing polymeric films (e.g., plastics) and non-polymericfilms. In addition, the present system can be used to test films orsubstrates of various thicknesses including substrates with a thicknessof up to 1 mm or higher. The substrates can be, for example, polymericplaques, metal sheets, paper sheets, or other composite materials.Therefore, the terms “film,” “film sample,” or “film of material” areused herein to encompass various types of materials (e.g., plastic,paper, metal, or composites) and various thicknesses of the materials.In one instance, the system allows the testing of other fabricatedmaterials, such as those formed through injection molding, and otherplastic-forming means.

As it can be appreciated from the following paragraphs, the systemaccording to an embodiment of the present disclosure accomplishes a setof tasks in an efficient manner. The tasks include measuring a thicknessof the film sample; visually analyzing the film for defects in ameasurement region that would affect the analysis; measuring the film'sstrength and energy dissipation under impact; loading the film sampleinto a testing station, testing the film; and removing the tested filmfrom the testing station. In an embodiment, the system allows measuringthe thickness of a film at a position described by ASTM F1306; analyzingthe film for defects in the dart impact measurement region using acamera and machine vision analysis techniques; loading the film into thetesting station using a system that ensures separation of films forconsistent loading; performing a dart impact analysis of the filmsample; and performing automated calculation of results.

FIG. 1 shows a schematic diagram of a system according to an embodimentof the present disclosure. In an embodiment of the present disclosure,the system for analyzing impact and puncture resistance 10 includes oneor more of a robotic system 12, a material holder system 14, a materialthickness measurement system 16, a material image analyzer system 18,and a dart testing system 20. The robotic system 12, the material holdersystem 14, the material thickness measurement system 16, the materialimage analyzer system 18, and the dart testing system 20 can be locatedon a work surface 22 or common framework. The robotic system 12, thematerial holder system 14, the thickness measurement system 16, thematerial image analyzer system 18, and the dart testing system 20 can becontrolled using computer system 24. A delivery system may also beprovided. The delivery system may include one or more trays whichdeliver samples to a work surface where the robotic system 12 andmaterial holder system 14 may retrieve the film sample from the one ormore trays.

FIG. 2 shows a three-dimensional perspective view of a robotic system12, according to an embodiment of the present disclosure. In anembodiment, the robotic system 12 is a six-axis robotic arm system suchas Epson C4L robot made by Epson Corporation. According to embodiments,the Epson C4L robot system has a maximum reach of 900 mm (˜35″). Therobotic system 12 is configured to move a film sample to be analyzed ortested between stations provided on a work surface 22 or commonframework. For example, the robotic system can be connected to amaterial holder system, as described below in connection with FIG. 3.Other types of robotic systems besides the robotic arm shown in FIG. 2can be used to move a film sample between stations provided on the worksurface 22.

FIG. 3 shows a three-dimensional perspective view of a material holdersystem, according to an embodiment of the present disclosure. Thematerial holder system 14 is connected to one end of the robotic system12 shown in FIG. 2. For example, in an embodiment, the material holdersystem 14 is attached to an arm of the robotic system 12 usingfasteners. The material holder system 14 is configured to hold and movethe film sample. In an embodiment, the material holder system includes avacuum suction system 30 adapted to hold the film sample through vacuumsuction. In an embodiment, the vacuum suction system 30 includes twopairs of suction cups 32 configured to hold the film samplesubstantially flat on each corner of the film so as to prevent film sag.In an embodiment, the vacuum suction system further includes a thirdpair of suction cups 34 so as to increase the efficiency with which thefilm samples are moved around the work surface. For example, byproviding a third pair of suction cups 34, a previously tested filmsample 36 can simultaneously be picked up while a new film sample 38 isplaced for testing.

Although suctions cups are described herein as being used to hold thefilm sample, other mechanisms or systems can also be used to hold thefilm sample depending on the type of material. For example, the suctioncups may be well suited for holding non-porous and relatively lightsamples, such as various plastics and polymer materials. Therefore, if,for example, porous materials are used, then the suction cups may bereplaced by other holding mechanisms such as magnets, clips, or someother type of gripping mechanism.

FIG. 4 shows a three-dimensional perspective view of the components of athickness measurement system, according to an embodiment of the presentdisclosure. The thickness measurement system 16 is configured to measurea thickness of the film sample in a wide range of thicknesses, forexample between 0.5 mil (12.7 micrometer) to 10 mil (250 micrometer).The thickness measurement system 16 is configured to measure a thicknessof the film using a contact plate 40 and a probe 41. The contact plate40 and the probe 41 are generally flat and contact the film on opposingsurfaces thereof, and the thickness of the film is measured as thedistance between the contact plate 40 and the probe 41. The surface ofboth the contact plate 40 and the probe 41 is sufficient to avoidpuncturing the film sample during the measurement. The contact plate 40and probe 41 have the benefit of spreading out the force of thethickness gauge and preventing the film sample from becoming deformedduring the measurement. For example, the contact plate 40 and probe 41can be configured to be used for materials that are flexible and pliableor for more rigid samples.

The thickness measurement system 16 also includes a high-accuracydigital contact sensor 44 (for example, Keyence GT2 Series from KeyenceCompany). The sensor 44 is used to measure the thickness of the filmsample to an accuracy of 1 micron (0.04 mil). The sensor 44 is selectedfor its accuracy. The probe 41 is mechanically linked to the sensor 44.The thickness measurement system 16 also includes a ramp 42 that isarranged so that the film sample (not shown) does not catch on eitherthe top or bottom contacts of the sensor 44. Once the film is in placebetween contact plate 40 and probe 41, pressurized air from air-pressuresystem 46 is applied to the sensor 44 that extends shaft 45 linked tosensor 44 and to probe 41 to move the probe 41 to measure the thicknessof the film.

Although a mechanical type thickness measurement system 16 is describedand used, other types of thickness measuring systems can also beemployed. For example, in another embodiment, the thickness measurementsystem 16 includes laser distance measuring sensors adapted to determinethe thickness using laser beams. For example, dual laser thicknessanalyzers can be used to measure a thickness of the film sample. In yetanother embodiment, capacitive measurement systems can be used tomeasure a thickness of the film. Capacitive (or generally impedance)measurement systems are based on measuring the capacitance (orimpedance) across the material.

Referring back to FIG. 1, before or after thickness measurement at thethickness measurement system 16, the film sample is moved by the roboticsystem 12 to the material image analyzer system 18. FIG. 5 shows athree-dimensional perspective view of a material image analyzer systemfor analyzing defects in the film sample, according to an embodiment ofthe present disclosure. In an embodiment the material image analyzersystem 18 is based on the principle of polarized light. The term“defect” is used herein to include any imperfections or irregularitiesin the film sample. The material image analyzer system 18 is configuredto detect defects in a film sample to be tested. A source of polarizedlight 18A is used to illuminate the film within the analyzer system 18,while eliminating any ambient light. After the light passes through thefilm, it is captured by a camera 18B fitted with a polarizing filter. Aperfectly formed film does not scatter the polarized light from thesource thus resulting in a completely clear image. However, anyimperfections/defects in the film scatters light that are detected bythe camera. A machine vision algorithm then identifies and tags filmswith significant defects. Therefore, the material image analyzer system18 is based on detecting defects caused when polarized light passingthrough the film sample is affected by certain physical defects presentin a sample. Because the material image analyzer system relies onpolarization of light, when the material to be tested is changed, thepolarization may also change which would potentially indicate a defectto be present where there is none. However, as part of the analysisaspect, defect or irregularity analysis is shifted to the datainterpretation and is conducted by looking at the range of results froma film and identifying the outliers based on standard deviation anddistance from the mean. Therefore, the present method of determiningdefects is independent of the material and is a more universal solutionto the problem. In an embodiment, alternatively, the material imageanalyzer system 18 may include a gel tester that is configured toquantitate and identify the types of defects. Examples of gel testersinclude optical control system (OCS) testers. Other types of materialimage analyzer systems than the one described above can alternatively beused. For example, optical light transmittance analyzer systems orultrasound defect detection systems can be used to detect defects in afilm sample.

Following the defect analysis, the film sample is moved by the roboticsystem 12 to the dart testing system 20. The dart testing system isconfigured to test the physical characteristics of a film sample. In anembodiment, the physical characteristics include elasticity and strengthof the film sample. Referring to FIGS. 6A and 6B, the dart testingsystem 20 includes a film clamping system 60. FIG. 6A is athree-dimensional perspective view of the clamping system 60, accordingto an embodiment of the present disclosure. FIG. 6B shows a cut-awayview of the clamping system 60, according to an embodiment of thepresent disclosure. The film clamping system 60 plays a role in ensuringthe accuracy of the test. The clamping system 60 includes two jaws 62Aand 62B. In an embodiment, the jaws 62A and 62B are circular, i.e., havea circular or annular shape. However, the jaws 62A and 62B can also havea different shape such as a polygonal shape. In an embodiment, the twojaws 62A and 62B comprise corresponding surface geometries thatcompletely or partially mate with one another when the jaws 62A, 62B areclosed against one another. For example, as shown in the cut-away ofFIG. 6B, the upper jaw 62A is provided with a pattern of grooves 64A andridges 65A. The lower jaw 62B is provided with matching grooves 64B andridges 65B. The ridges 65A in the upper jaw 62A are configured to matewith grooves 64B in lower jaw 62B. Ridges 65B in the lower jaw 62B areconfigured to mate with grooves 64A in upper jaw 62A. The grooves 64A,64B and ridges 65A, 65B are configured to pull the film taut when thetwo jaws 62A, 62B close on each other. The grooves 64A, 64B and ridges65A, 65B are further configured so that no undue stresses are applied onthe film in the process. In an embodiment, the grooves and ridges arecircular. In an embodiment, a width of a ridge is slightly smaller thana width of a groove so as to provide sufficient space for the filmsample to be caught between, but not cut by, the opposing ridges andgrooves. The jaws 62A and 62B define a centrally located aperture, suchas a hole 66. In an embodiment, the central hole 66 is 3″ (7.6 cm) indiameter (specified by the ASTM testing standard). The two jaws 62A and62B are actuated by a parallel jaw pneumatic gripper 68 (obtained fromSchunk) that can be actuated to open and close the jaws 62A, 62B. In anembodiment, the bottom jaw 62B includes four suction cups 63 (shown inFIG. 6A) that hold the film in place while the film clamping system 60is open. Other clamps than shown in FIGS. 6A and 6B can be used to holdthe film sample during the dart test. In an embodiment, a pressurebetween 10 psi (0.68 bar) and 50 psi (3.45 bar), e.g., 15 psi (1.03 bar)is applied by the parallel jaw pneumatic gripper 68 to close the twojaws 62A and 62B to hold the film sample therebetween. However, otherpressures are possible provided the applied pressure does not shear thefilm sample.

The functionality of the clamp assembly 60 is tested to confirm that (a)the film sample is pulled taut when the clamp closes and there is noundue stress/stretching of the film due to the clamp and (b) the filmsample does not slip in the clamp throughout the testing process. A highspeed camera system is used to help gather qualitative data for thesestudies.

To test the efficacy of the clamp assembly 60 to pull the film taut,multiple film samples with varying levels of wrinkles and creases areplaced in the clamp for different tests. High-speed video is capturedfrom above the clamp assembly 60 as it closes on the film.

FIGS. 7A and 7B show the initial and final frames of a video of the filmsample clamped by the clamp assembly 60, according to an embodiment ofthe present disclosure. The initial frame in FIG. 7A shows some wrinklesin the film. However, upon closure of the clamp system 60, the finalframe in FIG. 7B clearly shows that the film has been pulled taut.Concentric circles were drawn on the film sample before the film samplewas placed in the clamp assembly 60. The frames also show that thecircles are not significantly altered in shape when the clamp assembly60 closes. Therefore, the clamp assembly 60 does not negatively impactthe film sample while pulling it taut.

After the film sample is secured by the clamp assembly 60, a dart ismoved through the film sample and again, a high-speed video of the testis captured. FIGS. 8A and 8B show frames from the film sample when thedart just strikes the film (FIG. 8A) and when the film is stretched themost (just before puncture) (FIG. 8B), according to an embodiment of thepresent disclosure. The two frame images in FIGS. 8A and 8B show thatthe edges of the film sample closest to the clamp jaws remain in placeindicating that the film sample does not slip in the clamp assembly 60.The above tests were performed on relatively thin (0.5 mil or 12.7micrometer) and relatively thick films (10 mils or 254 micrometer) andin both cases the conclusions were the same.

Referring to FIG. 9, the dart testing system or device 20 also includesa dart probe mechanism 90. FIG. 9 shows a three-dimensional perspectiveview of the dart probe mechanism 90, according to an embodiment of thepresent disclosure. The dart probe mechanism 90 includes a dart probe 92and a propulsion system 94 that moves the dart probe 92. In anembodiment, the propulsion system 94 includes a linear motor 96 (e.g., aLinMot linear motor from LinMot USA, Inc.) and a controller (not shown)to control the linear motor 96. The linear motor 96 is configured forrelatively high acceleration and deceleration while accurately followinga prescribed motion profile. In an embodiment, the linear motor providesthe flexibility to vary or select a target speed of the dart probe fromrelatively lower speeds (0.04 m/s) to relatively higher speeds (4 m/s)as well as regulate the speed during a puncture resistance and dartimpact test while reaching the target velocity within the allowablerange of motion. Furthermore, the linear motor provides the benefit ofquick and easy retrieval of the dart probe as the dart probe is linkedto the linear motor. The controller can use a conventionalproportional-integral-derivative (PID) controller with feed-forwardcompensation based on estimated motor parameters. Instructions are sentto the controller by the computer system 24 (see, FIG. 1). The computersystem 24 is in communication with the controller and the computersystem 24 is configured to send a command signal to the controller tocontrol the linear motor 96. The computer system 24 is configured tosend a command signal to the controller to load a trajectory and to movethe dart probe 92 according to the loaded trajectory. Similarly,feedback data are received by the computer system 24 from the PIDcontroller. The dart probe 92 is attached to a movable slider 95 of thelinear motor 96, while the stator is secured to the work surface 22 orframe, for example, by post 97. Because the dart probe 92 is controlledby the linear motor 96, the retrieval process for dart probe 92 isfaster and safer than with prior art systems, making possible automated,high-throughput film testing. However, propulsion systems other than thelinear motor 96 can be used to move the dart probe 92. For example, ahydraulic system or pneumatic system (e.g., using compressed air) canalso be used to move the dart probe 92. A motor can also be used insteadof the linear motor 96 to move the dart probe 92.

The dart testing system of device 20 further includes a force sensor 99.The force sensor 99 is configured to measure a force that the dart probe92 is subjected to during a movement of the dart probe 92. In anembodiment, the force sensor 99 is a piezoelectric force sensor that isinstalled at a bottom of the dart probe 92, for example between the dartprobe 92 and a slider 95 of the motor 94, to measure a force signalduring a dart test. Piezoelectric sensors are capable of measuringfast-changing forces accurately. Piezoelectric sensors are well suitedfor measuring the force form the dart probe 92 which involves afast-changing force profile. Although a piezoelectric sensor is usedherein to measure forces during the dart tests, other types of sensorscan also be used to measure the forces.

A dart impact test correlates to the ASTM D1709 standard while apuncture resistance test correlates to the ASTM F1306 standard. The darttesting system 20 is configured for a better velocity regulation andfaster probe retrieval. By interchanging the dart probe 92, the darttesting system 20 can perform a puncture resistance test at low speedand a dart impact test at a higher speed.

FIG. 10 shows a three-dimensional perspective view of a dart probe,according to an embodiment of the present disclosure. In an embodiment,the dart probe 92 is built as specified by the ASTM testing standards.In an embodiment, the dart probe 92 is a cylindrical rod 102 with a 0.5″(1.27 cm) in diameter. In an embodiment, the cylindrical rod 102 has adiameter between 0.2″ (0.51 cm) and 1″ (2.54 cm). The dart probe 92 alsohas a hemispherical end 104, as specified by the ASTM standard. Thehemispherical shape minimizes stress concentration. According to anembodiment, the hemispherical end 104 can have a radius of 0.25 inches(0.63 cm), as specified by the ASTM testing standard. While the ASTMstandard specifies that the probe be made of steel, this would make theprobe heavy. Therefore, in an embodiment, to minimize the weight of thedart probe 92, the dart probe 92 is constructed to be hollow.Additionally or alternatively, the dart probe 92 is made of Aluminum. Toensure that the dart probe 92 complies with the ASTM standard, the tip104 can be made from steel. In an embodiment, the tip 104 is fastened,using for example glue, or screwed, to the cylindrical rod 102. Theoverall length of the probe is about 10″ (25.4 cm). In an embodiment,the overall length of the probe is between 6″ (15.2 cm) and about 16″(40.6 cm). The weight of the dart probe 92 is approximately 90 g. In anembodiment, the weight of the dart probe 92 is between 50 g and 200 g.

To perform a high speed dart impact test, ASTM standards require thatthe dart probe travels at 3.3 m/s, preferably substantially constant, atthe moment of impact with the film sample to be tested, and continues totravel at no less than 80% of that speed until the film sample ispunctured. In an embodiment, the velocity of the dart probe 92 is 3.3m/s at impact with the film sample and the velocity remains more than80% of 3.3 m/s until the film sample is punctured by the dart probe 92.To achieve this speed profile over a reasonable travel distance, carefulplanning of the trajectory may be needed. There are three phases to thetrajectory: acceleration from rest to 3.3 m/s before contact with thefilm sample, constant velocity of 3.3 m/s, and deceleration from 3.3 m/sto rest after the film sample is punctured. Due to acceleration anddeceleration, the force sensor 99 records the G-forces in theacceleration and deceleration phases. The data from the acceleration anddeceleration phases are discarded as will be explained further in thefollowing paragraphs. Ideally, these forces would not exist in theconstant velocity portion of the trajectory and would not contaminatethe force measurements due to the probe's impact with the film sample.However, if the acceleration profile is too aggressive, the PID positioncontrol system cannot keep up with the target position initially, andeventually overshoots the target velocity in the constant velocityregion. This produces an oscillation in the motion of the dart that isreflected in the force sensor 99. In order to avoid this undesirablesituation, a smooth trajectory can be established to minimize suddenchanges in acceleration. The gains on the PID controller can be adjustedto ensure that the system is over-damped or non-oscillatory. Althoughthe velocity of the dart probe 92 is described above as being equal to3.3 m/s at impact, the velocity of the dart probe 92 can be adjustedfrom a relatively low 0.04 m/s to perform puncture resistance tests to 4m/s to perform high speed dart impact tests.

FIGS. 11A and 11B show views of the film sample clamped by the clampjust before the dart comes into contact with the film sample and afterthe dart comes in contact with the film sample and stretches the filmsample to a maximum just before puncture, respectively, according to anembodiment of the present disclosure.

To keep testing conditions substantially the same for all film samplesto be tested, a common film format is selected for the test samples. Forexample, in one embodiment, a 6″×6″ (15.2 cm×15.2 cm) piece of film isselected as the common format. For example, this size is large enough tobe securely held in the 3″ (7.6 cm) diameter clamp 60 for the dart test.Furthermore, a conventional die is available to cut films in thisformat. However, as it can be appreciated, other sizes and formats canalso be used.

An exemplary the testing procedure for the dart system includes thefollowing steps:

-   -   (a) picking up a film sample by the robotic system 12 using the        material holder system 14, as shown in FIG. 14,    -   (b) measuring a thickness of the film sample using the material        thickness measurement system 16, as shown in FIG. 15,    -   (c) placing the film sample in the clamp 60 in the dart testing        system 20, as shown in FIGS. 17A and 17B. FIG. 17A shows the        robotic system 12 picking up a tested film sample from the dart        testing system 20. FIG. 17B shows the robotic system 12 placing        a new untested film sample in the dart testing system 20.    -   (d) moving the dart probe 92 in the dart testing system 20,    -   (e) collecting data and results of the dart test by the computer        system 24, and    -   (f) disposing of the tested film sample, as shown in FIG. 18.    -   Optionally, the test procedure can also include performing a        defect analysis on the film sample using material image analyzer        system 18, as shown in FIG. 16

The sample can comprise a 6″ (15.2 cm) square film.

With respect to step (a), a 6″ (15.2 cm) square film can be placed on asample receptacle and a test sequence is initiated. The robotic system12 picks up the film sample using the material holder system 14. In anembodiment, the pick-up motion is performed at an appropriate speed toavoid dropping of the film sample.

With respect to step (b), the robotic system 12 moves the film to thethickness measurement system 16. In an embodiment, two separatemeasurements are made by the thickness measurement system 16. A firstmeasurement is performed with no film sample present to obtain a zeroreading and a second measurement is performed with the film sample inplace. The difference between the second and the first measurementsprovides the thickness of the film sample. By measuring zero value foreach reading, the thickness measurement system 16 can account for anylong term drift/build-up in the sensor. However, measuring the zerovalue may also be performed once if there is confidence in the zerovalue (i.e., the zero value does not change from measurement tomeasurement). Alternatively, the zero value may be measured after aplurality of measurements or at regular periods of time to take intoaccount any potential drift that may occur with time.

With respect to step (c), when the film sample is ready for testing, theclamp 60 of the dart testing system 20 is opened and the material holdersystem 14 attached to the robotic system 12 first removes any old filmthat is in the clamp 60 (if a film is present in the clamp) and places anew film sample in the clamp 60. As depicted in FIG. 3 and FIGS. 17A and17B, this is accomplished by controlling vacuum suction cups 34 on thematerial holder system 14 to grab and remove any used/tested film 36from the clamp 60 (see, FIG. 17A) and by controlling the pair of vacuumsuction cups 32 to hold the new film sample 38 and placing the new filmsample 38 between the two jaws 62A and 62B of the clamp 60 (see, FIG.17B) while still holding the tested/used film 36 with vacuum suctioncups 34. By using the pair of vacuum suction cups 34, a previouslytested film sample 36 can simultaneously be grabbed and picked up whilea new film sample 38 is grabbed and placed for testing. This increasesthe efficiency of the overall system. Instead of moving the roboticsystem 12 to remove a tested film and then to place a new film samplefor testing, a single move of the robotic system 12 picks up the testedfilm sample while at the same time places a new film sample for testing.The set of suction cups 63 on the clamp 60 (see, FIG. 6A) are thencontrolled to hold the film sample 36 in place between the two jaws 62Aand 62B. The already tested film sample is removed by moving thematerial holder system 14 with the robotic system 12 and placing it inan area for disposal, as shown in FIG. 18. Once the robotic system 12with the material holder system 14 withdraws from the space of clamp 60,the clamp 60 is closed and the placed new film sample is held tautbetween the jaws 62A and 62B of the clamp 60. Thus, the new film sampleis ready to be tested.

With respect to step (d), the linear motor 96 (see, FIG. 9) isinitialized when the system is started including homing of the linearmotor 96 (see, FIG. 9) to a consistent starting position. In anembodiment, once the linear motor 96 is initialized, multiple tests canbe run without re-initializing the linear motor 96. In an embodiment,the linear motor 96 of the dart testing system 20 can be re-initializedperiodically, e.g., daily, to insure that the linear motor 96 returns toa same starting position. The dart probe 92 of the dart testing system20 is then moved by the computer system 24 instructing the PIDcontroller of the dart testing system 20 to load a specified trajectoryand to send a command to the linear motor 96 to move the dart probe 92.

With respect to step (e), a command is also sent by the computer system24 to a data acquisition system in communication with the computersystem 24 and in communication with the force sensor that measures aforce signal during a dart test to start data collection. This commandcan be sent substantially simultaneously with the moving of the dartcommand, or can also be sent sequentially with the moving of dartcommand. After the testing is complete, the motor returns to its initialposition.

With respect to step (f), the used film sample can then be lifted by thematerial holder system 14 using the robotic system 12 and placed in atrash bin which can be periodically emptied by an operator. Thiscompletes the cycle and the system returns to its initial state, readyto pick up a next film sample, e.g., from or when it arrives at thereceptacle.

According to an embodiment, the robotic system 12 moves the film sampleto the material image analyzer system 18. As described in the aboveparagraphs, an image of the film is captured through a polarizing filterwhile illuminated with polarized light. The image can be stored forfurther analysis (either automated image analysis or manual analysis ata later time) to determine whether the film sample has any defect, orany defect that would materially affect the test results.

In addition to controlling the dart test and collecting data and resultsof the dart test, in an embodiment, the computer system 24 can befurther configured to track the film sample as it progresses throughvarious tests, such that the thickness measurement, defect analysis, anddart test information is correlated for each sample and stored for laterreference and analysis. Thus, for example, test data from a defectivesample can be flagged and evaluated whether it should be relied on ordiscarded.

Typically, the time from impact to the puncture of the film sample is inthe order of a few milliseconds. In addition, Fast Fourier analysis ofthe acquired impact signal showed a frequency information content ofabout 20 kHz. Therefore, the sampling frequency (data collection rate)may be performed at higher than 20 kHz. The frequency spectrum of thedata captured shows relevant data at lower frequencies and any noise athigher frequencies. The noise can be eliminated using low-pass filters.

As stated above, sensors are used to measure the force that the probe issubjected to. In an embodiment, a single-axis force sensor is used tomeasure the force in the dart system. As explained above, in anembodiment, a piezoelectric sensor is selected due to its high bandwidth(36000 Hz) and hence its ability to measure fast changes in force. In anembodiment, a single-axis force sensor from PCB Piezotronics, model ICPForce Sensor, 208C02 is chosen. This piezoelectric sensor has a loadcapacity of 100 lb. (equivalent to a force of 444 N) in the Z-direction.This sensor is configured for dynamic force applications. Any staticload on the sensor will eventually return to zero.

In an embodiment, to confirm the speed of the dart at impact and throughthe process of puncturing the film, the dart velocity is calculated bytaking the numerical derivative of the position signal. To eliminate anynumerical noise introduced by this process, a low-pass filteringstrategy is used similar to the one used for filtering the force signal.

In an embodiment, the computer system 24 in communication with the darttesting system 20 is configured to collect or acquire force data fromthe dart testing system 20. In an embodiment, data collection in thedart testing system 20 begins when the dart is moved and ends when thedart comes to a stop at the top of its stroke. This ensures that delaysand timing considerations do not impact the data collected while thedart is in contact with the film sample. Therefore, in order to isolatethe relevant portions of data within the collected data, the collecteddata is preferably truncated. This is performed using the data from theimpact sensor that indicates the time at which the dart makes contactwith the film. Completion of puncture is indicated when the measuredforce falls to zero. However, due to filtering of the force signal, theforce may not drop to zero. Therefore, in an embodiment, the puncturecomplete point is identified using the unfiltered force signal.

FIG. 12A is a plot of the force (N) exerted on the probe versus time (s)from a start of the movement of the probe to a complete stop of theprobe, according to an embodiment. This plot shows a first broad peakcorresponding to the acceleration of the probe, a sharp peakcorresponding to the contact of the probe with the film sample and asecond broad peak corresponding to the deceleration of the probe.

FIG. 12B is a plot of the force (N) exerted on the probe versus time (s)from the impact point with the film sample to completion of puncture ofthe film sample, according to an embodiment of the present disclosure.

TABLE 2 Metric Units Description Calculation Peak Force N Maximum forceIdentifying the maximum value experienced by the film of force afterimpact of the dart sample during the test. probe with the film samplePeak mm Displacement of the Subtracting the displacement Displacementfilm sample when the of the dart probe at the point of peak force isobserved. impact with the film sample from the displacement of the dartat peak force. Peak Energy J Energy absorbed by Area under the force-the film sample when displacement curve up to the peak force is observedpoint of maximal force. Total mm Displacement of the Point of completepuncture of Displacement film sample at the point the film sample isidentified as of complete puncture of the point when the force the filmreturns to zero after reaching its maximal value Total Energy J Totalenergy absorbed Area under the complete force- by the film sampledisplacement curve

Scientists look for a few key metrics calculated from the force datacollected by the dart system. These metrics help characterize the filmsbased on their applications. These metrics are summarized in Table 2along with their units, description and a brief description of how theyare calculated.

FIG. 13A shows a plot of the force (N) versus displacement (m),according to an embodiment of the present disclosure. On FIG. 13A isindicated the peak of the force or maximum force and the peak energycorresponding to the area under the force curve up to the maximum force.The energy corresponds to the integral of the force to the distance ordisplacement. In an embodiment, a trapezoid method is used to computethe energy or integral of the force. However, as it can be appreciatedother computing methods can be used.

FIG. 13B shows a plot of the force (N) versus displacement (m),according to an embodiment of the present disclosure. On FIG. 13B isindicated the peak of the force or maximum force and the total energycorresponding to the area under the force curve up to the totaldisplacement.

After all replicates or film samples of a single type of film have beentested, a statistical algorithm is used to detect and eliminate anyoutliers in the data. The purpose of eliminating any statisticaloutliers is to eliminate any incorrect test results that may result fromimproper testing (e.g., no film present during test, torn film, etc.).Hence, the thresholds used to eliminate outliers are conservative.

In an embodiment, once the outliers are identified, the mean andstandard deviations of the remaining replicates or samples in the dataset can be calculated and uploaded to a database. Outlier data can betagged as such and can be stored in the database for further review ifdesired.

The term “computer system” is used herein to encompass any dataprocessing system or processing unit or units. The computer system mayinclude one or more processors or processing units. The computer systemcan also be a distributed computing system. The computer system mayinclude, for example, a desktop computer, a laptop computer, a handheldcomputing device such as a PDA, a tablet, a smartphone, etc. A computerprogram product or products may be run on the computer system toaccomplish the functions or operations described in the aboveparagraphs. The computer program product includes a computer readablemedium or storage medium or media having instructions stored thereonused to program the computer system to perform the functions oroperations described above. Examples of suitable storage medium or mediainclude any type of disk including floppy disks, optical disks, DVDs, CDROMs, magnetic optical disks, RAMs, EPROMs, EEPROMs, magnetic or opticalcards, hard disk, flash card (e.g., a USB flash card), PCMCIA memorycard, smart card, or other media. Alternatively, a portion or the wholecomputer program product can be downloaded from a remote computer orserver via a network such as the internet, an ATM network, a wide areanetwork (WAN) or a local area network.

Stored on one or more of the computer readable media, the program mayinclude software for controlling a general purpose or specializedcomputer system or processor. The software also enables the computersystem or processor to interact with a user via output devices such as agraphical user interface, head mounted display (HMD), etc. The softwaremay also include, but is not limited to, device drivers, operatingsystems and user applications. Alternatively, instead or in addition toimplementing the methods described above as computer program product(s)(e.g., as software products) embodied in a computer, the methoddescribed above can be implemented as hardware in which for example anapplication specific integrated circuit (ASIC) or graphics processingunit or units (GPU) can be designed to implement the method or methods,functions or operations of the present disclosure.

The invention claimed is:
 1. A system for analyzing a physicalcharacteristic of a film sample, the system comprising: a materialholder system configured to hold the film sample; a dart testing systemconfigured to test a physical characteristic of the film sample; and amoving system configured to move the held film sample to be analyzed ortested between stations, wherein the moving system is configured to movethe held film sample in the material holder system to the dart testingsystem from a different station.
 2. The system according to claim 1,wherein the moving system comprises an articulating-arm robotic system.3. The system according to claim 1, wherein the material holder systemincludes a vacuum suction system configured to hold the film throughvacuum suction, wherein the film sample has a quadrilateral shape withfour corners and the vacuum suction system comprises a first pair ofsuction cups and a second pair of suction cups configured to hold thefilm sample substantially on each corner of the film sample.
 4. Thesystem according to claim 3, wherein the vacuum suction system comprisesa first pair of suction cups and a second pair of suction cupsconfigured to hold and place the film sample to be tested, and a thirdpair of suction cups configured to pick up a previously tested filmsample.
 5. The system according to claim 1, further comprising amaterial thickness measurement system configured to measure a thicknessof the film sample.
 6. The system according to claim 5, wherein thematerial thickness measurement system comprises a probe configured tomeasure a thickness of the film sample over a spread area to avoidpuncturing the film sample during the measurement.
 7. The systemaccording to claim 1, wherein the dart testing system comprises aclamping system having an upper jaw and a lower jaw, wherein the upperjaw and the lower jaw each comprise grooves and ridges, and ridges inone of the upper and lower jaw are configured to fit into grooves of theother of the upper and lower jaw.
 8. The system according to claim 7,wherein one of the upper jaw and the lower jaw comprises a holdingmechanism configured to hold the film sample in place while the clampingsystem is open.
 9. The system according to claim 1, wherein the darttesting system comprises a dart probe mechanism configured to test aphysical characteristic of the film sample.
 10. The system according toclaim 9, wherein the dart probe mechanism comprises a dart probe and apropulsion system configured to move the dart probe.
 11. The systemaccording to claim 10, wherein the propulsion system comprises a linearmotor.
 12. The system according to claim 9, wherein the dart probemechanism comprises a piezoelectric force sensor connected to the dartprobe, the piezoelectric force sensor being configured to measure aforce signal during a dart test of the film sample.
 13. The systemaccording to claim 1, further comprising a computer system incommunication with the dart testing system, the computer system beingconfigured to acquire force data from the dart testing system.
 14. Thesystem according to claim 1, further comprising a material imageanalyzer system configured to detect a defect in the film sample.
 15. Amethod for analyzing a physical characteristic of a film sample, themethod comprising: holding the film sample by a material holder systemconnected to a moving system; moving the film sample by the movingsystem to a dart testing system from a different station; and testing aphysical characteristic of the film of the material using the darttesting system.
 16. The method according to claim 15, wherein testingthe physical characteristic of the film sample comprises holding thefilm sample taut and unstressed during the testing using a clampingsystem of the dart testing system.
 17. The method according to claim 15,wherein testing the physical characteristic of the film sample comprisespuncturing the film sample with a dart probe of the dart testing systemand measuring a force during testing of the film sample.
 18. The methodaccording to claim 15, further comprising: moving the film sample by themoving system from the dart testing system to a material thicknessmeasurement system; and measuring a thickness of the film sample usingthe material thickness measurement system.
 19. The method according toclaim 15, further comprising: moving the film sample by the movingsystem from the dart testing system to a material image analyzer system;and detecting a defect in the film sample using the material imageanalyzer system.
 20. A method for analyzing a physical characteristic ofa film sample, the method comprising: picking up the film sample by arobotic system connected to a moving system; moving the film sample bythe moving system to a dart testing system; placing the film sample bythe robotic system in a clamp of the dart testing system; testing aphysical characteristic of the film of the material using the darttesting system; picking up the film sample by the robotic system fromthe clamp of the dart testing system; and moving the film sample by themoving system from the dart testing system to another station.